Method and apparatus for controlling sleep disorder breathing

Abstract

A method and device for controlling sleep disorder breathing utilizes variable multiple level pressures. A pressure source supplies compressed breathable gas at a relatively low pressure to the user's airway. Pressure transducers monitor pressures and convert them into electrical signals. The electrical signals are filtered and processed to extract specific features such as duration and energy levels. If these features exceed selected threshold values for duration and energy level over a minimum period of time, then the microprocessor declares the presence of sleep disorder breathing. If a selected number of these events occur within a selected time period, then the microprocessor adjusts the pressure delivered by the pressure source. If sleep disorder breathing is not detected within a certain time period, then the microprocessor lowers the pressure level gradually. The device and method disclosed in this patent is capable of detecting apnea, hypopnea, and pharyngeal wall vibration. Further, it is able to distinguish between obstructive, central and mixed apnea and hypopnea.

What is claimed is: 
     
       1. A method of controlling sleep disorder breathing in a person, the method comprising the steps of: connecting an interface from a source of compressed air to a person's breathing passages;   supplying compressed air from the source of compressed air through the interface to the person's breathing passages;   measuring flow related variables and pressure variables of the compressed air in the interface;   detecting indications of sleep disorder breathing by comparing the measured flow related variables and the measured pressure variables to a sleep disorder breathing threshold;   responsive to the detection of indications of sleep disorder breathing, adjusting pressure of the compressed air while continuing to monitor the measured flow related variables and the measured pressure variables for sleep disorder breathing; and   updating the sleep disorder breathing threshold continuously on the basis of previously measured pressure and flow variables.   
     
     
       2. A method as set forth in claim 1, wherein the step of detecting indications of sleep disorder breathing includes: computing a running mean of a series of measured flow related variables;   setting a hypopnea threshold based on a fraction of the running mean for the measured flow related variables; and   comparing a value determined over an interval of samples for the measured flow related variable against the hypopnea threshold for indication of sleep disorder breathing.   
     
     
       3. A method as set forth in claim 1, wherein the step of detecting indications of sleep disorder breathing includes: computing a standard deviation value for the measured flow related variables over an interval;   periodically determining if the computed standard deviation value exceeds a standard deviation threshold; and   comparing the computed standard deviation value with the standard deviation threshold over a certain time interval to establish occurrence of pharyngeal wall vibration.   
     
     
       4. A method as set forth in claim 1, wherein the step of detecting indications of sleep disorder breathing includes: computing a mean over an interval of measured flow related variables; and   comparing the mean from the computing step to an apnea threshold.   
     
     
       5. A method as set forth in claim 1, wherein the measured flow rate variables include a measurement of pressure difference along the interface and the step of detecting indications of sleep disorder breathing includes: accumulating a plurality of mean pressure difference measurements;   accumulating a plurality of pressure measurements;   calculating energy values for the accumulated measurements of pressure differences and pressure;   determining a phase difference between the pressure measurements and the pressure difference measurements; and   comparing the energy values and the phase difference to thresholds to determine full or partial closure of a patient's breathing passages.   
     
     
       6. A method as set forth in claim 1, wherein the step of detecting indication of sleep disorder breathing further includes: determining if the measured flow related variable exceeds a threshold for an interface off condition;   responsive to an affirmative determination of the interface off condition, signaling the interface off condition;   absent determination of an interface off condition, determining if a pressure difference mean baseline exceeds a threshold for an interface leak condition; and   responsive to an affirmative determination of an interface leak condition, signaling the interface leak condition.   
     
     
       7. The method as set forth in claim 1, wherein the step of detecting sleep disorder breathing further includes: comparing a baseline calculation and a standard deviation calculation for a plurality of samples of measured pressure related variables against a plurality of a thresholds for failure of supply of compressed air.   
     
     
       8. An apparatus for controlling sleep disorder breathing in a person comprising: a source of pressurized breathable gas;   an interface connecting the source of breathable gas to a person's breathing passages;   at least one sensor coupled to the interface for measuring flow related variables and pressure related variables of the pressurized breathable gas in the interface;   detection means for comparing the measured flow related variables and the measured pressure variables to a sleep disorder breathing threshold, and responsive to the detection of indications of sleep disorder breathing, adjusting pressure of the compressed air while continuing to monitor the measured flow related variables and the measured pressure variables for sleep disorder breathing;   calculation means for updating the sleep disorder breathing threshold continuously on the basis of previously measured pressure and flow variables.   
     
     
       9. The apparatus as set forth in claim 8 in which the interface comprises: a mask adapted to be fit over the person's breathing passages; and   a conduit connecting the mask to the source of pressurized breathable gas.   
     
     
       10. The apparatus as set forth in claim 9 in which the pressure sensor comprises: a mask pressure sensor disposed in the mask; and   a conduit pressure sensor disposed in the conduit a selected distance from the mask pressure sensor.   
     
     
       11. The apparatus as set forth in claim 8 in which the source of pressurized breathable gas comprises a blower.